With as many as 150,000 drivers already on the Northway every weekday, continued growth could soon make traveling from Saratoga County to Albany unbearable, a new report for the state Department of Transportation concludes.

"Forecasts show that, unless corrective actions are taken, congestion and delays will continue to worsen throughout the combined I-87/US 9 corridor, and grow to intolerable levels, as the Capital District's population and employment opportunities grow," the report says.

The study by a New York City-based planning firm, Parsons Brinckerhoff, outlines options to improve traffic flow between Saratoga County and Albany, despite challenges like the narrowness of the Thaddeus Kosciusko Bridge and the more than 400 driveways that dot Route 9.

The report suggests using variable message boards that alter the speed limit and direct motorists toward alternate routes during congestion. It calls for considering carpool lanes, traffic lights that limit how many cars can enter the Northway at one time, and possibly a toll for an express lane on the Northway, an option DOT spokeswoman Carol Breen acknowledges would be unpopular.

The 75-page report is meant to outline all available options, she said, and the state is not committed to any of them.

"It is an extremely high-travel corridor. We really needed to focus on where we can do better," she said. "We're really still in the discussion phase. These are some of things that need to be addressed. We need to bring the public in at this point."

A meeting for residents to discuss the report will be 5:30 to 7:30 p.m. Tuesday at Colonie's library, 629 Albany Shaker Road.

"We're trying to look at things that can be done without huge, major, costly infrastructure projects," Breen said. "We're not going to add a fourth lane to the Northway."

Traffic along the Northway peaks at 150,000 vehicles a day between exits 5 and 6 in Colonie. The general volume is closer to 120,000 to 130,000 vehicles a day, with the number dropping to 100,000 once past Exit 9 in the heavily populated Clifton Park/Halfmoon area.

At peak commuting times, speeds at several spots along the Northway drop below 20 mph.

In Europe, systems called active traffic management include overhead message signs to tell drivers to change lanes and that the speed limit has changed due to the congestion. A 2006 study showed that capacity increased and accidents dropped where the systems were used. Such systems have now been introduced in Seattle and Minneapolis.

In some areas along the Northway, drivers also could be allowed to use the shoulders as lanes during peak traffic volume.

"This option would require resolution of a number of issues," the report states. "For example, I-87 provides only 10 foot shoulders along most of its length in the study area but no shoulders are present on the Twin Bridges."

Drivers would still need room to pull over if their cars break down, Breen said.

The report focuses a great deal more on the Northway than Route 9. Breen said that's because the state only has to worry about traffic on the highway, while Route 9 involves land use issues among the various towns.

"We don't want to make more traffic problems on Route 9," Breen said. The state also wants to avoid creating traffic impacts on side roads, she said.

"A lot of what we're considering for Route 9 is better managing traffic," she said. "Transit is going to be big focus on Route 9. If we can encourage more efficient systems that people will use, it can become an efficient tool."

The report says electronic messages could help there too.

"A series of route guidance signs should be placed along Route 9 that have a dynamic element allowing the signs to indicate the path that (a) motorist should follow to divert around the observed congestion," the report said: Alternate routes should be based on actual travel time so drivers don't find the alternate path takes longer than if they had stayed put.

The state DOT also is asking for legislation requiring drivers in fender benders to move their vehicles off the roadway.

While drivers typically stay where they are so police can examine the scene, Breen said, investigators can reconstruct accidents without having to see where cars landed. By removing the cars to the side of the road, she said, it increases safety and keeps traffic moving.

The state has no timeline for when it might turn the report's options into concrete actions. "It's really going to be taking the public input and digesting it," Breen said.